It is well known that the operation of steaming yarn consists essentially of heating said yarns in a humid environment in order to fix the torsions whereto the filaments making up the yarn had previously been subjected. In general this operation of steaming also follows an operation of dyeing in order to confer the required colour to the yarns treated in this way.
Traditionally, in order to subject the yarn to these two operations, the yarn was first of all wound on a first cop for steaming, consisting of a cylindrical element having a lateral yarn winding wall which is solid and radially contractible when hot in order to adapt to the contraction which the yarn wound thereon undergoes during this operation, while for the subsequent dyeing operation it was necessary to use a different cop having a perforated lateral surface, suitable for the dye to pass through, in order to obtain uniform colouring of the yarn wound thereon. To avoid this need to unwind the yarn from cops intended for steaming in order to wind them on those intended for dyeing, cops have been provided which are suitable for both operations. These cops comprise essentially a perforated lateral wall capable of contracting radially.
Said cops are also housed for performing the abovementioned operations in autoclaves and stacked one on top of the other. They must therefore have a structure which, in addition to being radially contractable, is also sufficiently rigid and stable in order to withstand the considerable axial loads whereto it is subjected.
Known radially collapsible perforated cops consist essentially of a cylindrical body for supporting yarn positioned between two end annular elements and which is defined by peripheral longitudinal rods which are all identical one to the other.
Said longitudinal rods are essentially of two types: either they are rods which can be deformed in a transverse direction and are connected one to the other by rigid spacers, wherein the transverse deformation of the rods is provided by portions thereof which deform on the thrust of said rigid spacers, or they consist of rigid elements connected via intermediate deformable elements which themselves provide the radial contraction of the cop. For example said longitudinal rods consist of elements with a "V" section which deform in order to generate said radial contraction of the cop by the plastic rotation of the branches of said "V", or in other cases are connected by intermediate elements formed by deformable "V"'s.
Whatever the manner of providing longitudinal rods defining the surface for winding the yarn and which are all identical one to the other, it is necessary, in order to confer sufficient rigidity and structural stability to the cop, to have longitudinal rods which are all of considerable size or which are arranged densely, too close one to the other and thus forming in both cases a considerable obstacle to the passage of the dye through the cop.
In order to overcome this disadvantage it was decided to perforate said longitudinal rods, although in this case too, in order not to weaken the cop excessively, use had to be made of cops with dimensions which are too small for solving the abovementioned problem satisfactorily.
Another disadvantage shown by some types of known cops consists of the fact that the radial contraction therein involves the risk of nipping of the wound yarn with the danger of breakage of the yarn itself.
In other types of known cops, during the phase of radial contraction, due to the excessive stiffening of the attachment between longitudinal rods and end flanges, said longitudinal rods break at the attachment to the end flanges of the cop.
A further problem presented by known radial contraction cops for dyeing consists of the fact that the surface of winding of the yarn has the same diameter as the end flanges of the cop. This entails the risk that in parts the yarn detaches from the cop on which said yarn is wound loosely, via which the dye leaks longitudinally and does not therefore pass through the lateral surface of the cop, that is to say through the yarn, involving a loss of liquid intended for dyeing with subsequent decrease in dyeing efficiency and the risk of uneven colouring of the yarn.
The object of the present invention is that of providing a cop for the winding of yarns which is radially compressible and has a structurally stable lateral surface with a sufficiently high percentage of holes to allow the passage of considerable quantities of the dyeing liquid.
Another object of the present invention is that of providing a radially collapsible cop which avoids the risks of nipping of the yarn and risks of breakage of elements of the cop during the phase of contraction of the same.
A further object of the present invention is that of providing a radially collapsible cop wherein the previous disadvantages of leakage or longitudinal percolation of the dyeing liquid have been eliminated.